Pls help!! Just bought S7 Edge dual sim model SM-G935FD gold coloured from Ebay. Phone was shipped from Hong Kong, and it was sealed with "MIDDLE EAST & NORTH AFRICAN SIM CARD ONLY".
Didn't seem to care at first and inserted Indonesian SIM card, working perfectly with LINE chat, Whatsapp call and internet browsing, but when making phone call there is no sound coming in/out.

Checked all hardware, working fine. Also, not locked out of the SIM access since all data working perfectly. Local Samsung Service Center has suggested to reset the Samsung Firmware, is this safe? Will it solve the problem?